Modern Otto-cycle engines, in particular so-called FlexFuel engines, which can be operated with any desired fuel composition of gasoline and ethanol, exhibit increased introduction of fuel into the oil circuit of the Otto-cycle engine. This introduction of fuel has an adverse effect on the lubricating action of the engine oil. In particular, the subsequent outgassing of the fuel from the engine oil poses an acute risk to fault-free engine running. It is thus sought, in terms of hardware, to discharge the fuel again as quickly as possible. In terms of software, a fuel content of the engine oil is modeled. If one additionally takes into consideration systems of the Otto-cycle engine which must process a wide variety of fuels (for example fuels with different ethanol/water contents), the modeling of the introduction and discharge behavior becomes significantly more complex.
Correct introduction and discharge behavior for different fuels must be determined over the lifetime of the vehicle. Furthermore, the mixture of the different fuels must be taken into consideration. Only in this way is it possible to ensure correct system intervention or correct handling of a certain level of oil dilution and fuel outgassing.
Normally, the oil dilution and the fuel outgassing are determined by way of simple models which operate based on a lambda controller or which merely count the number of cold starts, with the oil dilution being inferred based on said number.